1. Field of the Invention
The invention relates to a marine anchor and, more specifically, to a twin-fluke, lightweight, high performance aluminum alloy anchor.
2. Description of Related Art
U.S. Pat. No. 4,892,053 twin-fluke anchor describes an improved aluminum anchor having a shank, a stock, and a pair of flukes coupled together by a crown structure and having the holding power of heavier steel anchors.
When a twin-fluke anchor rests on an underwater bottom, an anchor line or rode connects a boat or other marine vessel floating on the surface to an outer end of the anchor shank. The anchor rode pulls the anchor forward along the bottom as the marine vessel drifts with the wind or tide. The crown structure of the anchor, resting on one of its two crown plates, tends to resist the forward motion and elevates an aft end of the anchor thereby tipping the anchor to orient the anchor fluke tips downward towards the underwater bottom surface. As the anchor draws forward, the flukes bury themselves into the bottom surface. And with increase force on the rode, the flukes continue to bury themselves deeper into bottom to provide greater holding power. Typically, an anchor buries itself several feet under the bottom surface, particularly in muddy or sandy underwater bottoms.
The holding power of an anchor depends in part upon the underwater bottom surface condition. Most underwater bottoms consist of firm, good holding ground, such as sandy bottoms. But in calm bays and estuaries where silt and vegetable sediment accumulate, the bottoms consist of soft mud which provides poor holding ground for anchors.
The holding power of a twin-fluke anchor also depends upon the anchor's shank/fluke angle, i.e., the angle between the shank and the effective surface of the flukes. By increasing the shank fluke angle from a standard angle of approximately 30 to 35 degrees to an angle of approximately 40 to 55 degrees, the anchor substantially increases its holding power in poor holding ground, such as muddy bottoms.
In good holding ground, however, the standard shank/fluke angle of 30 to 35 degrees is necessary to set the anchor. If the angle is greater than about 35 degrees, for example if the shank/fluke angle is 45 degrees, the fluke tips drag along the firm underwater bottom and have difficulty initially digging into the surface to bury themselves. Further, when digging in at the increased angle, the planar portion of the flukes become caked with ground which substantially reduces the anchor's holding power.